We're having ours at the de Vere in Theobalds, Cheshunt - it's stunning.
Have you tried shuttleworth? It is between Bedford and Biggleswade and you have the option of marrying in the manor house (it is very grand!) Or in the swiss gardens there. It is a beautiful venue & if I wasn't having a church wedding (2 miles from shuttleworth) then I would have probably got married there.
Good luck with your search & all the planning for your big day
I come from Hertfordshire, we got married at Offley Place inbetween Luton-Hitchin, it's more Hitchin way though.
What style of venue, and budget are you looking at?
We looked at:
Whipsnade Zoo - you get photos with giraffes and all guests get to go on the train around the zoo.
Ashridge - amazing if you want that fairytale/country castle type wedding (pricey with it!)
Latimer House - house which has been converted to a hotel so all guests can stay onsite. Nice orangery for wedding breakfast.
Didn't go with any of the above as decided to get married up in leicestershire instead (where we live as opposed to herts where i grew up).
If you want reception only and a bit of an 'out there' theme then google North Hill Farm B&B - they have teepees! http://www.countryfieldweddings.co.uk
I've looked at Tudor Barn in Burnham, a lovely out of the way venue with good access to motorways and excellent staff. I've also booked the Bucks violinist and pianist Simon Jordan to play for me and the Bucks photographer David Bostock.